Understanding Video Quality – Pixels (p), Bitrate (kbps), Aspect Ratios

Some of the most common questions I get asked on video quality are-

  • I want my videos in 1080/720/480/360 p like Youtube. How does VdoCipher enable that?
  • What does kbps mean? How much bandwidth will 1 hour 1000 kbps video consume?
  • How many video quality options I need to have to ensure smooth playback across the world?
  • Why does VdoCipher provide bitrate (kbps) as quality options and not pixels (p)?
  • What is the size of a video for a certain pixel quality? (Say 1 hour 1080p video)

Here are some key definitions and concepts to help everybody better understand video quality parameters.

Pixels (p) – 1080 / 720 / 480 / 360 / 240 p

Pixels as a quality index essentially mean the height of video in number of pixels. Thus, a video quality at 1080p means – the height of video is 1080 pixels. Now the next question is what is the width of video? There is no exact technically right answer but in common convention, the video is 16:9 for online playback. Thus the width of video becomes 1080*16/9 – 1920 pixels.

So, in common convention 1080p means 1080 pixels as the height of video and 1920 as the width of video. Similarly, 480 p will mean 480 pixels in height and 480*16/9 -853 pixels as width of video. Though this may vary if the aspect ratio of video is different (like 4:3). So, until you know the aspect ratio, you cant determine the exact number of pixels in a video.

Does pixel directly correspond to a size? What will be the size of 1 hour,1080 p video?

Surprisingly there is no fixed answer to that. If pixel quality is fixed, then the number pixels in a video is fixed. E.g a 1080 p will have 1080*1920 = 2073600 pixels. But how much of data is captured in each pixel can vary and is determined by the streaming provider. Thus, Youtube , Vimeo and Vdocipher can provide different size of videos for the same length and same pixel quality. It is even possible that say 1 hour, 1080p video of vdocipher is of lower size than 720 p of Vimeo.

So, the next obvious question is what exactly determines the video size? It is bitrate (generally represented by kbps like 1500 kbps etc). Please read the next section to understand bitrate as a quality index.

Bitrate (kbps) – 1500/ 1000/ 600 /300 kbps

How is bitrate linked to the size of the video?

Bitrate is generally represented by kbps which essentially means kb (kilobytes) of data per second. So, the size of a 1hour 1500 kbps video will be – 1500*60*60 -kilobytes = 1500*60*60/8000 MBs of data = 675 MB per hour of video data.

Similarly, a 1000 kbps 1 hour video will be 450 MB in size , 600 kbps will be 270 MB in size.

What is the relation between pixels(p) and bitrate (kbps)?

There is no precise technical relation between pixels and bitrate. For the same streaming provider; higher the pixels, higher the bitrate and vice-versa. Though as I already mentioned different service providers can offer different pixels even at the same bitrate.

What bitrate/pixels does VdoCipher use for HD streaming?

VdoCipher has a wide range for 1080p HD in terms of bitrate. It depends on what size the customer uploads and what is type of content – Media, E-learning (In e-learning, if it is screen capture, animation or class recording etc.) It is at maximum kept at 1500 kbps for 1080p , for certain high motion movies it is kept at 2500 kbps. For certain cases, low motion lectures, 1080p can be as low as 600 kbps.

Why does Youtube use pixels as a quality parameter, while VdoCipher uses bitrate for the same?

There are two primary reasons –

  1. Bitrate directly corresponds to size and hence bandwidth consumption & costs. 1000 kbps video will consume double bandwidth as compared to 500 kbps video. Pixels don’t have such direct co-relation.
  2. VdoCipher can provide higher pixel quality even at low bitrates. So, for many cases , VdoCipher can provide 1080p or 720 p HD even at 500-900 kbps range. Thus, there is no need for a lower pixel parameter.

How many video quality options I need to have to ensure smooth playback across the world?

From VdoCipher experience –

  1. For Movies/Serials with a lot of motion – 3 or maximum 4 qualities. We typically do 2500 kbps, 1500 kbps ,900 kbps, 500 kbps Or something like 2000 , 1200, 600 kbps.
  2. For Educational content – 2 in most cases. 1500 kbps and 600 kbps. Or sometimes – 1500, 700, 300 kbps.

VdoCipher has customers across all 6 continents. (Sorry, we don’t have a customer in Antarctica yet :D) . The bitrate and quality optimizations are made keeping in mind slow connections of Asia & African users. Over the time, they have worked well for all geographical distributions ensuring a great viewing experience.

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